The main object of this work is to discover new general syntheses in the 8-azapurine, purine, and pteridine series, in order to facilitate the preparation of hitherto inaccessible poly-aza heteroaromatic compounds in these three families, for trial in the chemotherapy of cancer. The structure of new substances discovered in this work is being correlated with their physical and chemical properties as a necessary first step in providing correlations with biological properties. Special attention is being given to problems of chemical stability likely to affect the biological application of such substances. Specifically, the work is divided into seven research projects, four of them in the 8-azapurine series, two in the pteridine series, and one in the purine series. The 8-azapurine projects are (a) to study the degradative action of mild aqueous bases on 8-azapurines; (b) to devise new syntheses of 8-azapurines, substituted by one or more atom of sulfur, from 4-amino-5-cyano-1,2,3-triazoles, (c) to synthesize the highly strained 1- and 3- methyl derivatives of 8-azapurine, and (d) to insert an aldehyde group into the 5-position of 4-amino-1,2,3-triazoles and convert the products into new 8-azapurines. The pteridine projects are (a) to condense 2-aminopyrazine-3-carboxamide with amidines to obtain derivatives of pterid-4-one, and (b) to act with amidines (both N- and C- substituted) on 2-aminopyrazine-3-carbonitrile to obtain derivatives of 4-aminopteridine. The purine project is to obtain 1,6-dihydropurines (and, from these, purines) starting from 4-amino-5-cyanoimdazoles.